Cellular insertion of primary and secondary myotubes in embryonic rat muscles

Development ◽  
1989 ◽  
Vol 107 (2) ◽  
pp. 243-251
Author(s):  
M.J. Duxson ◽  
Y. Usson
Keyword(s):  
Ultrastructural Study ◽  
Muscle Tension ◽  
Electrical Coupling ◽  
Muscle Fibres ◽  
Tension Development ◽  
End To End ◽  
Developing Muscle ◽  
Two Populations ◽  
Unique Relationship ◽  
Adhering Junctions

Mammalian muscles develop from two populations of myotubes; primary myotubes appear first and are few in number; secondary myotubes appear later and form most of the muscle fibres. We have made an ultrastructural study to investigate how primary and secondary myotubes in embryonic rat muscles transmit tension during the period of their development. Primary myotubes extend from end to end of the muscle from the earliest times, and attach directly to the tendon. In contrast, newly formed secondary myotubes are short cells which insert solely into the primary myotubes by a series of complex interdigitating folds along which adhering junctions occur. As the secondary myotubes lengthen and mature, their insertion is progressively transferred from the primary myotube to the tendon proper. We suggest that this variable insertion of immature secondary myotubes, combined with complex patterns of innervation and electrical coupling in developing muscle, makes it difficult to predict the overall contribution of secondary myotubes to muscle tension development. This work extends other studies showing the unique relationship between a primary myotube and its associated secondary myotubes, indicating that these may constitute a developmental compartment.

Physiological features of the opercularis muscle and their effects on vibration sensitivity in the bullfrog Rana catesbeiana

1987 ◽  
Vol 131 (1) ◽  
pp. 189-204
Author(s):  
T. E. Hetherington
Keyword(s):  
Inner Ear ◽  
Slow Rate ◽  
Rana Catesbeiana ◽  
Muscle Tension ◽  
Isometric Tension ◽  
Sensory Function ◽  
Morphological Evidence ◽  
Muscle Fibres ◽  
Ground Vibrations ◽  
Tension Development

The amphibian opercularis muscle connects a movable otic element (the operculum) to the pectoral girdle and can act in reception of ground vibrations. Various physiological parameters of the opercularis muscle of the bullfrog Rana catesbeiana were measured and compared with similar measurements on the iliofibularis muscle of the hindlimb. The opercularis muscle is a very slowly contracting muscle, with a Vmax of 1.81 muscle lengths s-1 compared to a Vmax of 6.24 muscle lengths s-1 for the iliofibularis muscle. The opercularis muscle develops tension slowly, taking about 10 s to attain maximum isometric tension when stimulated at 100 Hz. The muscle can retain high levels of tension for several minutes, and following stimulation has a time to half-relaxation of about 4–6 s. The slow velocity of contraction, slow rate of tension development, fatigue-resistance and slow rate of relaxation of the opercularis muscle support morphological evidence that it consists mostly of tonic muscle fibres. Experiments were also made to examine the effects of muscle tension on reception of ground vibrations as measured by inner ear microphonics. Severing the nerve supplying the opercularis muscle produced slight decreases of no more than 2 dB in responses to vibrations from 25 to 200 Hz. Artificial stimulation of the opercularis muscle after severing the nerve supplying the muscle increased responses to vibration across the entire frequency range. Higher tension levels produced greater increases in responses; at the highest tensions used (about 120 kN m-2) responses were increased by as much as 4.5 dB. The opercularis muscle is therefore specialized for slow but prolonged contractions, and tension is important in its sensory function. A tensed opercularis muscle appears to transmit faithfully motion of the forelimb, produced by vibrations, to the operculum such that the latter moves relative to the inner ear fluids.

The Effects of Acclimation Temperature on a Neuromuscular System of the Crayfish, Astacus Leptodactylus

1979 ◽  
Vol 78 (1) ◽  
pp. 281-293
Author(s):  
MIKKO HARRI ◽  
ERNST FLOREY
Keyword(s):  
Membrane Lipids ◽  
Characteristic Temperature ◽  
Resting Membrane Potential ◽  
Acclimation Temperature ◽  
Muscle Fibres ◽  
Astacus Leptodactylus ◽  
Tension Development ◽  
Temperature Range ◽  
Wide Range ◽  
Warm Acclimation

1. Crayfish, Astacus leptodactylus, were acclimated to 12 °C and to 25 °C. Nerve muscle preparations (closer muscle of walking legs) were subjected to temperatures ranging from 6 to 32 °C. 2. The resting membrane potential of muscle fibres was found to increase with temperature in a linear manner, but with a change in slope at around 170 in cold-acclimated preparations, and around 24 °C in warm-acclimated ones. 3. Temperature acclimation shifted the temperature range of maximal amplitudes of fast and slow e.j.p.s toward the acclimation temperature. Optimal facilitation of slow e.j.p.s also occurred near the respective acclimation temperature. 4. E.j.p. decay time is nearly independent of temperature in the upper temperature range but increases steeply when the temperature falls below a critical range around 17 °C in preparations from cold-acclimated animals, and around 22 °C after acclimation to 25 °C. 5. Peak depolarizations reached by summating facilitated e.j.p.s are conspicuously independent of temperature over a wide range (slow and fast e.j.p.s of cold-acclimated preparations, fast e.j.p.s of warm-acclimated ones) which extends to higher temperatures after warm acclimation in the case of fast e.j.p.s. In warm-acclimated preparations the peak depolarization of slow e.j.p.s first falls then rises and falls again as the temperature increases from 8 to 32 °C. 6. Tension development elicited by stimulation of the slow axon at a given frequency reaches maximal values at the lower end of the temperature range in cold-acclimated preparations. The maximum is shifted towards 20 °C after warm acclimation. Fast contractions decline with temperature; possible acclimation effects are masked by the great lability of fast contractions in warm-acclimated preparations. 7. It is suggested that changes in the composition of membrane lipids may be responsible for the effects of acclimation on the electrical parameters and their characteristic temperature dependence.

Gradation of isometric tension by different activation rates in motor units of cat flexor carpi radialis muscle

1986 ◽  
Vol 56 (2) ◽  
pp. 494-506 ◽  
Author(s):  
B. R. Botterman ◽  
G. A. Iwamoto ◽  
W. J. Gonyea
Keyword(s):  
Muscle Tension ◽  
Motor Units ◽  
Isometric Tension ◽  
Medial Gastrocnemius ◽  
Potential Contribution ◽  
Tension Development ◽  
Stimulus Interval ◽  
Flexor Carpi Radialis ◽  
Single Motor Units ◽  
Activation Rates

Single motor units of the flexor carpi radialis (FCR) muscle were activated with a series of constant-rate stimulus trains to study the relation between the frequency of activation and isometric tension development (F-T relation). The tension produced by each stimulus train was expressed as a percentage of the maximum tension-time area (Amax) found for a given unit. Between 25 and 75% Amax a clear separation was seen in the rates needed to produce the same relative tension for the F-T curves of slow-twitch (type S) and fast-twitch (type F) units. Over the steepest portion of the F-T curve (25-50% Amax), where tension output was most sensitive to changes in activation rate, type F units required substantially higher stimulation rates (30 pps) to achieve the same relative tension output as type S units. Furthermore, the frequency range that corresponded to the steep portion of the curve was 2.3 times greater for type F units. For both type S and F units, twitch duration was deemed to be an important determinant of the F-T curve, as has been shown previously. A direct continuous relation was seen between the integrated twitch time (ITT) and the stimulus interval needed to produce 50% Amax (r = 0.94, P less than 0.001). Thus, units that had relatively brief twitches required higher activation rates to achieve the same relative percentage of Amax. Comparison of F-T curves from FCR with those derived by other investigators for cat hindlimb units (medial gastrocnemius and peroneus longus) revealed that significant differences in activation rates were needed to produce the same percentage of Amax throughout the midrange of the F-T curve. At 50% Amax, type F units in FCR required activation rates approximately 20 pps higher than type F units in the hindlimb. Type S units in FCR required only slightly higher rates (approximately equal to 5 pps). Based on a number of well-founded assumptions, F-T curves derived from FCR units were used to estimate the potential contribution of rate coding to total muscle tension by type S and F units. This analysis leads to the conclusion that rate modulation is a potentially important factor in the gradation of tension for the FCR muscle.

The Motor Innervation and Musculature of the Antennule of the Hermit Crab, Pagurus Alaskensis (Benedict)

1973 ◽  
Vol 58 (3) ◽  
pp. 767-784
Author(s):  
P. J. SNOW
Keyword(s):  
Hermit Crab ◽  
Muscle Tension ◽  
Low Frequency ◽  
Muscle Fibres ◽  
Intracellular Recordings ◽  
Motor Innervation ◽  
Postsynaptic Inhibition ◽  
Tonic Component ◽  
Whole Muscle ◽  
Tonic Tension

1. The motor innervation and musculature of the medial and distal segments of the hermit-crab antennule have been described anatomically. 2. Intracellular recordings within these muscles and simultaneous monitoring of whole-muscle tension have been used to define the motoneurones and contractile properties of the muscle fibres they innervate. 3. The motor system consists of two fast, two slow and one mixed muscle which are innervated by seven motoneurones. 4. The motor innervation is such that this system may be divided into three components: phasic, phasic-tonic and tonic. The possible involvement of these components in the antennular activities is discussed. 5. The tonic component is adapted to produce fine tonic tension in response to relatively low-frequency (5-10/sec) motoneurone discharge. It is suggested that this may be important for the postural control of appendages which, owing to the density of the environmental medium, are relatively weightless. 6. No evidence of postsynaptic inhibition was found, and this is discussed in relation to the movements of the antennule.

The Action of the Eyecup Muscles of the Crab, Carcinus, During Optokinetic Movements

1968 ◽  
Vol 49 (2) ◽  
pp. 223-250
Author(s):  
M. BURROWS ◽  
G. A. HORRIDGE
Keyword(s):  
Large Amplitude ◽  
Optokinetic Nystagmus ◽  
Wide Spectrum ◽  
Muscle Tension ◽  
The Other ◽  
Fibre Types ◽  
Muscle Fibres ◽  
Exact Form ◽  
Slow Movement ◽  
The One

1. The actions of the nine eyecup muscles of the crab during horizontal optokinetic movements are described. 2. Each muscle includes a wide spectrum of fibre types, ranging from phasic, with sarcomere lengths of 3-4 µm., through intermediate, to tonic fibres with sarcomeres of 10-12 µm. Each muscle receives at least one slow and one fast motoneuron, but no inhibitory supply. The slow axons predominantly innervate the tonic muscle fibres while the fast axons innervate the phasic ones. 3. Slow movement and the position of the eyecup in space are controlled by the frequency of slow motoneuron discharges. All muscles collaborate at every position. The phasic system is recruited during rapid eyecup movements of large amplitude. 4. In optokinetic nystagmus the exact form of the impulse sequences are described for each muscle. They are the consequence of a visually driven central programme which takes no account of the movement which it generates. Movements in opposite directions involve different central programmes; the one is not merely the reverse of the other. There is no effective proprioceptive feedback from the eyecup joint or from muscle tension receptors.

Potentiation of Neuromuscular Transmission by an Octopaminergic Neurone in the Locust

1979 ◽  
Vol 79 (1) ◽  
pp. 169-190 ◽  
Author(s):  
MICHAEL O'SHEA ◽  
PETER D. EVANS
Keyword(s):  
Indirect Effects ◽  
Neuromuscular Transmission ◽  
Time Course ◽  
Muscle Tone ◽  
Muscle Tension ◽  
Presynaptic Receptors ◽  
Extensor Muscle ◽  
Muscle Membrane ◽  
Muscle Fibres ◽  
Central Synapses

1. Spikes in the octopaminergic dorsal unpaired median (DUM) neurone which innervates the extensor tibiae muscle of the locust metathoracic leg (DUMETi) produce direct and indirect effects on muscle tension. 2. Direct effects include a slowing of an intrinsic rhythm of contraction and relaxation, a relaxation of muscle tone and a small hyperpolarization of the muscle membrane potential. The latter two effects are weak and variable. All three effects are mimicked by superfusion of octopamine and are mediated by octopamine receptors on the muscle fibres. 3. Indirect effects are found when the DUMETi neurone is stimulated at the same time as the motoneurones innervating the extensor muscle. They include (a) potentiation of tension generated in the extensor muscle by spikes in the slow excitatory motoneurone (SETi), (b) reduction in duration of each twitch contraction generated by SETi due to an increase in the rate at which the muscle relaxes, (c) increase in the amplitude of the synaptic potential generated by SETi. These various effects have a time course of several minutes and far outlast the duration of DUMETi stimulation. They can be mimicked by superfusion of octopamine. 4. The effect of DUMETi on neuromuscular transmission is mediated by receptors with a high affinity for octopamine located both on the muscle and on the terminals of the slow motoneurone. The presence of the presynaptic receptors is revealed by the increase in the frequency of spontaneous miniature end plate potentials recorded in the muscle in the presence of octopamine. 5. DUMETi is a member of a group of similar aminergic neurones and it is suggested that they may share a role in modulating transmission at peripheral neuromuscular synapses, and possibly central synapses.

Control of tension development in scallop muscle fibres with foreign regulatory light chains

Nature ◽  
1980 ◽  
Vol 286 (5773) ◽  
pp. 626-628 ◽  
Author(s):  
R. M. Simmons ◽  
A. G. Szent-Györgyi
Keyword(s):  
Light Chains ◽  
Muscle Fibres ◽  
Tension Development ◽  
Regulatory Light Chains
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